The Sleuth Kit (TSK) is a C library and a collection of command line tools. Autopsy is a graphical interface to TSK. TSK can be integrated into automated forensics systems in many ways, including as a C library and by using the SQLite database that it can can create.
The Sleuth Kit is a free, open source suite that provides a large number of specialized command-line based utilities.
It is based on The Coroner's Toolkit.